HP Virtual Connect 4Gb Fibre Channel Module for c-Class BladeSystem - Manual (Page 85)

Virtual Connect networks 85
Virtual Connect networks
Understanding networks and shared uplink sets
The VC-Enet modules use standard Ethernet bridge circuitry with special firmware so that they function as a
configurable Ethernet port aggregator. For a specific external data center connection, only the selected
server Ethernet NIC ports are visible on what appears to be an isolated, private, loop-free network. The
VC-Enet module uplinks do not participate in the data center Spanning Tree Protocol or other switch
management protocols that could disrupt the data center network.
The VC-Enet module uplinks support link aggregation, link layer discovery protocol (LLDP), and VLAN
tagging. VLAN tagging enables uplinks to be shared to carry multiple networks.
Each network defined within VCM can have one or more uplinks. Virtual Connect independently ensures that
no loops are created within the VC domain and that the resulting tree structure is optimized for the uplinks to
the data center.
When multiple uplinks are used on a network, VCM first verifies if any of the ports can be collected together
into an aggregation group, which requires connections to go from a single VC-Enet module to a single data
center switch. Then, VCM picks a single link (or aggregation group) as the connection to the external
network. The remaining connections are blocked and held as standby ports.
TIP: To improve network performance and prevent unnecessary Spanning Tree Topology
Change Notifications (TCN) on the network, configure Ethernet switches connected to Virtual
Connect with the same Spanning Tree settings you would use when connecting to a server blade
NIC. For Cisco switches, use the portfast command to enable ports connected to a VC-Enet
module. This action ensures that link state changes on Virtual Connect do not cause a TCN.
Shared uplink sets and VLAN tagging
A shared uplink set identifies VC-Enet module uplinks that carry multiple networks over the same cable or set
of cables. In this case, each Ethernet packet carries a VLAN tag (IEEE 802.1Q) to identify the specific
network to which it belongs. On shared uplinks, the VLAN tags are added when packets leave the
VC-enabled enclosure and are removed when packets enter the enclosure. The external Ethernet switch and
VCM must be configured to use the same VLAN tag identifier (a number between 1 and 4094) for each
network.
Virtual Connect places no special restrictions on which VLAN identifiers can be used, so the VLAN IDs
already used for the networks in the data center can be used on these shared uplinks. To configure a shared
uplink set for VLAN tagging, obtain a list of the network names and their VLAN IDs.
A shared uplink set enables multiple ports to be included to support port aggregation and link failover with
a consistent set of VLAN tags.
Because VLAN tags are added or removed when Ethernet packets leave or enter the VC-Enet shared uplink,
the VLAN tags have no relevance after the Ethernet packet enters the enclosure.